In recent years, bag-packed foods wherein bags are filled with ready-made or semi-cooked foods and the like and those are poured into the packaging bags made of heat resistant films and thus bag-packed foods are heated and cooked by a microwave oven just before eating, have widely come into the market.
Such packed foods for cooking use when heated directly by the microwave oven without opening, may possibly contaminate the inner side of the microwave oven by rupturing the packaging bag and scattering contents as a result of raising the internal pressure by generated steam and the like which is emitted from foods.
Accordingly, the rupture of the packaging bag has been prevented, for example, by opening a small air hole and the like or by cutting off a portion by use of scissors and the like to the packaging bag before cooking by the microwave oven, in order to avoid the increase of the internal pressure within the inner side of the packaging bag.
However, by such method, since the steam emitted after heating is released immediately to the outside of the packaging bag, the steam-cooking effect by the steam decreases and the deterioration of foods may occur as a result of an acceleration of food dehydration in the packaging bag.
Accordingly, a packaging bag is provided by a sealed package; wherein, for example, as shown in FIG. 17(a), a laminated film 101 is made as a cylindrical shape, and at the same surface side, the facing two-edge parts of the film are laid on each other in a butt-seam manner, and as shown in FIG. 17(b), the laid-on sides are joined by heat-sealing to form an easily peelable region in a part of the region throughout an entire length in a longitudinal direction, and a cylindrical body is formed by providing a predetermined width of a heat-sealing part 102, and after said heat-sealing part 102 is made to be one-sided to one edge side of the cylinder, and after the bag is fabricated by providing a bottom heat-sealing part 103 by heat-sealing a lower line part of the cylindrical body excluding the lower line part of the heat-sealing part 102, contents 105 are filled in from an upper line part of an opening part of the cylindrical body, and then as shown in FIG. 17(c), the upper line part of the cylindrical body is heat-sealed to provide a heat-sealing part 104 of the upper part excluding the upper line part of the heat-sealing part 102.
The packaging bag is described as capable to conduct the steam pressure relief, when the steam pressure of the internal bag is raised while heating, an easily peelable region which is made in a part of region in the heat-sealing part 102 delaminates to release the steam (JP09-150864, A (1997)).
Also, for a part of films of constituting the packaging bag, a device to use an air permeable film is proposed (JP10-129748, A (1998)).
Moreover, a device is proposed where a narrow seal width is provided to comprise a narrow seal width in a part of the region in a back seal part of the packaging bag and in the region of the narrow width part a cutting is made to form an opening which is capable to open by the internal pressure of the bag (JP11-278557, A (1999)).
The packaging bag, which is made so as to conduct the steam releasing from a part of the heat-sealed packaging bag film as an easily peelable state, is advantageous from the point of fabricating for the reason that different materials are not used, but even if such packaging bag is applied, when an appearance after heating is observed, a scattering of contents is found in the easily peelalble region provided in a part of the region of the heat-seal part of the packaging bag so that the scattering of the contents in the perfect state and a stain of the inside of the microwave oven are not considered to be avoidable.